In the production of elastomeric polymers, such as isobutylene-based elastomers, the product obtained from the polymerization process is often in the form of a slurry comprising the precipitated polymer and unreacted dissolved monomers in a solvent. The solvent and dissolved monomers are stripped from the precipitated polymer, with the polymer solids sent to a slurry tank. The water-slurried elastomer is then dewatered, and extrusion dried to form elastomer crumbs for bailing and/or packaging.
U.S. Pat. No. 5,729,911 discloses a process for continuous dewatering/drying of EP(D)M. The process comprises continuously charging wet EP(D)M crumb into a single screw extruder having particular structural features and conveying the wet crumb through the length of the extruder under conditions sufficient to expel water, increase the pressure across the die plate of the extruder and heat the crumb. The dried crumb thus extruded is characterized in that it contains less than 1% water.
However, processes for finishing EP(D)M elastomers may not work for other types of elastomers, such as isobutylene-based elastomers, and especially temperature sensitive halogenated isobutylene-based elastomers. Different elastomers have different slurry chemistries and different viscoelasticity which affect the ability to dewater and dry the elastomer. For example, a slurry of butyl elastomer, particularly halobutyl elastomer, has a higher pH than a slurry of EPDM. This higher pH makes the butyl elastomer crumb more slippery and thus harder to dewater and dry than EPDM crumb. Additionally, elastomer characteristics, such as Mooney viscosity, molecular weight distribution, and the presence or absence of long chain branching, may also affect the ability to dewater and dry the elastomer.
U.S. Pat. No. 4,909,898 (Padliya et al.) discloses a polymer finishing method wherein a slurry comprising a precipitated polymer and a volatile diluent is feed into a mixer/kneader to remove the volatile diluent. Padliya et al. teaches that an immiscible liquid must be added to the slurry.
Therefore, there still remains a need for improved processes for devolatizing and drying isobutylene-based elastomers. In particular, there is a need for a process and apparatus that is able to finish large capacities of isobutylene-based elastomers in a single finishing line.